Bond pad for flip chip package

ABSTRACT

A bond pad for a flip chip package. The bond pad is suitable for an integrated circuit chip. A plurality of slots are designed in the bond pad. Each of the slots extends along a direction which is perpendicular to a radial direction from the center of the bond pad. The bond pad is deposed at the corner of the integrated circuit chip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an integrated circuit packagingtechnology and in particular to a flip chip packaging technology.

2. Description of the Related Art

The flip chip package is the most space efficient package for very largescale integrated (VLSI) circuits. Flip chip technology is compatiblewith a variety of circuit board types, including ceramic substrates,printed wiring boards, flexible circuits, and silicon substrates. A flipchip is generally a monolithic semiconductor device, such as anintegrated circuit (IC), having bead-like terminals formed on one of itssurfaces. The terminals, usually in the form of solder bumps, serve toboth secure the flip chip to a circuit board and electricallyinterconnect the chip circuitry to a conductor pattern formed on thecircuit board.

In a flip chip package, an integrated circuit (IC) device usually has aplurality of bond pads distributed over the surface of the device in arectangular array. These bond pads are used to connect the IC device tothe electrical paths on a printed circuit board (PCB). A ball shapedsolder bump is formed on each of the bond pads of the IC device. The ICdevice and the PCB are positioned so that the solder bumps contact theelectrical paths on the PCB, and the assembly is heated to reflow thesolder, forming electrical and mechanical bonds between the IC deviceand the PCB.

Erickson, in U.S. Pat. No. 6,180,265, discloses a method for convertingan aluminum wire bond to a flip chip solder bump pad, so as to enable anIC device originally configured for wire-bonding attachment to bemounted using a flip chip attachment technique.

Chittipeddi et al., in U.S. Pat. No. 6,187,658 and in U.S. Pat. No.6,087,732, discloses a method of forming a bond pad for flip chippackage integrating the package process with the semiconductormanufacturing process.

The bond pads on the IC device are typically aluminum or analuminum-base alloy for various known processing and performance-relatedreasons. FIG. 1A shows a sketch cross-section of a portion of theconventional flip chip package. As well, the cross-section of the entirestructure of the conventional flip chip package is shown in FIG. 4. Itis understood that chip 100 is conventionally provided with bond pads102 and solder bumps 104. In order to clearly illustrate the structureof the flip chip package, only one bond pad 102 and one solder bump 104is shown in the figure. Heat is usually produced during operation of theIC device, causing the expansion of the bond pad 100 and the PCB 106.

However, the thermal expansion coefficient of the bond pad 102 is verydifferent from that of the PCB 106. As shown in FIG. 1B, the structureof the flip chip package subjected to the thermal stress is distorted.Thus, the solder bump 104 easily peels off.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a bond pad for aflip chip packaging, wherein the bond pad is structured to releasestress, especially thermal stress, such that peeling of the solder bumpcan be avoided.

One feature of the present invention is to provide slots in a bond padused in the assembly of a flip chip. When the slot extends along adirection which is substantially perpendicular to a radial direction ofthe center of the chip, same as thermal expansion direction, thermalstress can be released by the slot, such that solder bump peeling due tothe difference of the thermal expansion between the bond pad connectedwith the upper terminal of the solder bump and the PCB connected withthe lower terminal of the solder bump can be avoided. The heat producedby operation of the chip radiates from the center of the bond pad.Various embodiments of the orientation of the slots are describedhereinafter.

To achieve the above objects, an embodiment of the present inventionprovides a bond pad for a flip chip package. The bond pad is used in theassembly of a flip chip. The bond pad is provided with at least one slotextending along a direction which is perpendicular to a radial directionfrom the center of the integrated circuit chip. The bond pad is deposedat the corner of the integrated circuit chip.

According to the present invention, the bond pad with the designed slotcan be preferably located substantially at corners of the integratedcircuit chip. Also, the number of the bond pad can be more than one,thus the bond pad is preferably arranged substantially in an array.

According to the present invention, the bond pad is circular orrectangular.

According to the present invention, the slot is preferably rectangular.The slots in the same bond pad are parallel to each other when thenumber of the slots is more than one. The slot extends at leastpartially through the bond pad.

Another embodiment of the present invention provides a plurality of bondpads for a flip chip package. The bond pads are used in the assembly ofa flip chip. The bond pads are located in each of the quadrants of theintegrated circuit chip. Each of the bond pads comprises at least oneslot, and each of the slots in the same quadrant extends along adirection which is substantially perpendicular to the diagonal lines ofthe integrated circuit chip passing through the quadrant in which it islocated.

According to the present invention, the slot is rectangular. Each of theslots extends at least partially through the bond pad. The slots in thesame quadrant are parallel to each other.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIGS. 1A through 1B are cross-sections illustrating the thermalexpansion problem of the conventional flip chip package;

FIGS. 2A through 2B are top-views showing the bond pad for a flip chippackage according to one embodiment of the invention, wherein at leastone bond pad is deposed at the corner of the integrated circuit chip;

FIGS. 3A through 3B are top-views showing the bond pad is for flip chippackage according to another embodiment of the invention, wherein aplurality of bond pads are located in each of the quadrants of theintegrated circuit chip, each of the bond pads has at least one slot,and each of the slots in the same quadrant extends along a directionwhich is substantially perpendicular to the diagonal line of theintegrated circuit chip passing through the quadrant in which the bondpads are located;

FIG. 4 is a cross-section showing the flip chip package according to oneembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are now described withreference to the figures.

FIG. 4 shows a cross-section of the conventional bond pad structure. Thebond pad structure is constructed on a semiconductor substrate 500.Multilayers comprising interlayer dielectric layers (ILD) 502, 504 aredisposed on the semiconductor substrate 500. A lower metal pad 518 isinterposed in the interlayer dielectric layers (ILD) 502. An upper metalpad 510 is disposed on the interlayer dielectric layers (ILD) 504 andsurrounded by a passivation layer 506. The upper metal pad 510 and thelower metal pad 518 are electrically connected by a plurality of plugs512. A bond pad 514 is disposed on the upper metal pad 510. A solderbump 516 is further disposed on the bond pad 514 for flip chip packageusing known solder bumping reflow techniques. The substrate 500 isunderstood to possibly contain IC devices, such as MOS transistors,resistors, logic devices, and the like, though they are omitted from thedrawings for the sake of clarity. In the following, the term “substrate”is meant to include devices formed within a semiconductor wafer and thelayers overlying the wafer. The term “substrate surface” is meant toinclude the uppermost exposed layers on a semiconductor wafer, such as aSi wafer surface, an insulating layer and metal wires. The interlayerdielectric layers (ILD) 502, 504 may comprise SiO₂, phosphosilicateglass (PSG), boro-phospho silicate glass (BPSG), and low k materials,such as fluorinated silicate glass (FSG). The passivation layer 506 maycomprise silicon nitride. The metal pads 510, 518 may comprise Cu, Al ora Cu/Al alloy. As well, the bond pad 514 may comprises Al or an Al basedalloy.

During the operation of the IC device, a large amount of heat isproduced, inducing shear stress. The thermal generally radiates from acenter position of the surface of the IC device. The solder bump andbond pad is subjected to the shear stress. According to the presentinvention, the conventional bond pad architecture described above may beutilized. However, the surface of the bond pad of the present inventionis patterned to reduce the solder bump shear stress. According to anaspect of the present invention, a plurality of slots which aresubstantially perpendicular to the radiate direction from the center ofthe surface of the IC device are provided in the bond pad to release theshear stress. Several embodiments of the arrangements of the bond padare described hereafter in accordance with the present invention.

First Embodiment

In FIGS. 2A through 2B, the integrated circuit chip 200 is a rectangleshape substrate. The center C of the integrated circuit chip 200 isdefined by the intersection of the diagonals of the integrated circuitchip 200. The integrated circuit chip 200 preferably comprises aplurality of bond pad 204 having at least one slot 202 extending along adirection which is perpendicular to a radial direction T from the centerC. The bond pad 204 are preferably located substantially at corners ofthe integrated circuit chip 200. The integrated circuit chip 200 canfurther comprise additional bond pads 210, as shown in FIG. 2B, whereinall the bond pads 204 and 210 are preferably arranged in an array. Thebond pads 204 can comprise a single slot 202 or a plurality of slots202. The slots 202 are preferably parallel to each other when the numberof the slots is more than one. The bond pad 204 can be a rectangular orcircular-shaped structure. The slot 202 preferably is rectangular. Theslot 202 extends at least partially through the depth of bond pad 200.

The slots 202 may be formed by known photolithography and etchingmethods.

The slots 202 extend along a direction which is substantiallyperpendicular to a radiate direction from the center of the surface ofthe integrated circuit chip 200. Thereby, thermal stress can be releasedby the slots 202, such that solder bump peeling due to the thermalexpansion difference between the bond pad connected with the upperterminal of the solder bump and the PCB connected with the lowerterminal of the solder bump can be avoided.

Second Embodiment

In FIGS. 3A and 3B, an integrated circuit chip 400 is used in theassembly of a flip chip. The integrated circuit chip 400 comprises aplurality of bond pads 404 a, 404 b, 404 c, and 404 d locatedrespectively in each of the quadrants of the integrated circuit chip400. Each of the bond pads 404 a, 404 b, 404 c, and 404 d comprises atone slot 402 extending along a direction T which is substantiallyperpendicular to the diagonal line of the integrated circuit chip 400passing through the quadrant in which it is located. All the slots 402disposed in the same quadrant extend along the same direction. Forexample, all of the bond pads 404 a extend along a direction, and all ofthe bond pads 404 b extend along another direction. The bond pads 404 a,404 b, 404 c, and 404 d can be arranged substantially in an array. Asshown in FIG. 3A, the bond pads 404 a, 404 b, 404 c, and 404 d can be acircular-shaped. As shown in FIG. 3B, the bond pads 404 a, 404 b, 404 c,and 404 d can also be a is rectangle-shaped.

The slot 402 preferably is rectangular. The slots 402 of a pattern areparallel to each other when the number of the slots is more than one.The slot 402 extends at least partially through the depth of bond pads404 a, 404 b, 404 c, and 404 d.

The slots 402 may be formed by known photolithography and etchingmethods.

The slots 402 extend along a direction which is substantiallyperpendicular to a radiate direction from the center of the surface ofthe integrated circuit chip 400. Thereby, thermal stress can be releasedby the slots 402, such that solder bump peeling due to the thermalexpansion difference between the bond pad connected with the upperterminal of the solder bump and the PCB connected with the lowerterminal of the solder bump can be avoided.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A bond pad for a flip chip package, suitable for an integratedcircuit chip, comprising: at least one slot extending along a firstdirection, which is perpendicular to a second direction radiating fromthe center of the integrated circuit chip.
 2. The bond pad as claimed inclaim 1, wherein the bond pad is located substantially at corners of theintegrated circuit chip.
 3. The bond pad as claimed in claim 1, whereinthe patterns are arranged substantially in an array.
 4. The bond pad asclaimed in claim 1, wherein the bond pad is circular or rectangular. 5.The bond pad as claimed in claim 1, wherein the slot is rectangular. 6.The bond pad as claimed in claim 1, wherein the slot extends at leastpartially through the bond pad.
 7. The bond pad as claimed in claim 1,wherein the slot extends down to the bottom of the bond pad.
 8. A bondpad for a flip chip package, suitable for an integrated circuit chip,comprising: a plurality of parallel slots located in the bond pad, eachof the slots extending along a first direction, which is perpendicularto a second direction radiating from the center of the integratedcircuit chip, wherein the bond pad is disposed at the corner of theintegrated circuit chip.
 9. The bond pad as claimed in claim 8, whereinthe bond pad is circular or rectangular.
 10. The bond pad as claimed inclaim 8, wherein the slot is rectangular.
 11. The bond pad as claimed inclaim 8, wherein the slot extends at least partially through the bondpad.
 12. The bond pad as claimed in claim 8, wherein the slot extendsdown to the bottom of the bond pad.
 13. A bond pad structure for a flipchip package, suitable for an integrated circuit chip, the integratedcircuit chip having a rectangular shape, comprising: a plurality of bondpads located in each of the quadrants of the integrated circuit chip,wherein each of the bond pads comprises at least one slot and each ofthe slots in the same quadrant extending along a direction which issubstantially perpendicular to the diagonal lines of the integratedcircuit chip passing through the quadrant in which it is located. 14.The bond pad as claimed in claim 13, wherein the patterns are arrangedsubstantially in an array.
 15. The bond pad as claimed in claim 13,wherein the slot is rectangular.
 16. The bond pad as claimed in claim13, wherein the slot extends at least partially through the bond pad.17. The bond pad as claimed in claim 13, wherein the slot extends downto the bottom of the bond pad.
 18. The bond pad as claimed in claim 13,wherein the bond pad is circular or rectangular.
 19. A semiconductordevice, comprising: a substrate; a conductive layer, disposed on thesubstrate; and at least one bond pad, disposed on the conductive layer,wherein the bond pad comprises at least one slot extending along a firstdirections which is perpendicular to a second direction radiating fromthe center of the surface of the substrate.
 20. The bond pad as claimedin claim 19, wherein the number of the bond pads located in eachquadrant of the integrated circuit chip is more than one, and each ofthe slots in the same quadrant extending along a direction which issubstantially perpendicular to the diagonal lines of the integratedcircuit chip passing through the quadrant in which it is located. 21.The bond pad as claimed in claim 19, wherein the slot is rectangular.22. The bond pad as claimed in claim 19, wherein the slot extends atleast partially through the bond pad.
 23. The bond pad as claimed inclaim 19, wherein the slot extends down to the bottom of the bond pad.24. A bond pad for a flip chip package, suitable for an integratedcircuit chip, comprising: a slot extending along a first direction,which is perpendicular to a second direction radiating from the centerof the integrated circuit chip, wherein the slot is rectangular.
 25. Thebond pad of claim 24, wherein the bond pad is deposed at the corner ofthe integrated circuit chip.
 26. The bond pad of claim 24, wherein theslot is one of a plurality of parallel slots located in the bond pad.27. The bond pad of claim 26, wherein each of the slots is rectangular.28. The bond pad of claim 26, wherein: the slot is one of a plurality ofslots located in quadrants of the integrated circuit chip; and each ofthe slots in the same quadrant extending along a direction, which issubstantially perpendicular to a diagonal line of the integrated circuitchip passing through the quadrant in which each of the slots is located.29. The bond pad of claim 28, wherein the integrated circuit chip isrectangular.
 30. A semiconductor device, comprising: a substrate; aconductive layer disposed on the substrate; and bond pads disposed onthe conductive layer; wherein: at least one of the bond pads comprisesat least one slot extending along a direction perpendicular to a radialdirection from the center of the surface of the substrate; each quadrantof the integrated circuit chip comprises at least two of the bond pads;and slots in the same quadrant extend in a direction that issubstantially perpendicular to the diagonal line of the integratedcircuit chip passing through the quadrant in which each of the slots islocated.
 31. The semiconductor device of claim 30, wherein the substrateis rectangular.
 32. The semiconductor device of claim 31, wherein theslots are rectangular.